Matching network circuit and Radio-Frequency Power Amplifier with Odd Harmonic Rejection and Even Harmonic Rejection and Method of Adjusting Symmetry of Differential Signals

ABSTRACT

A matching network circuit for RF power amplifier circuit capable of odd harmonic rejection and even harmonic rejection in the differential mode and the common mode, respectively. The matching network circuit includes a differential mode filter with a differential resonant frequency and a passive component coupled to a virtual short circuit node at the differential mode filter, wherein a common mode filter with a common resonant frequency includes the differential mode filter and the passive component. As a result, two notch filters with different resonant frequencies are utilized for the common mode and the differential mode, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/259,668, filed on Nov. 25, 2015, the contents of which areincorporated herein.

BACKGROUND

Differential modes operation is usually used for common mode noisesuppression. It can be used in many circuits such as a power amplifier(PA), a low noise amplifier (LNA), a mixer, and so on. However, thedifferential operation is not the mechanism for supporting multiplecommunication standards or multiple frequency bands.

The power amplifier is often required to provide a high swing and a lowoutput impedance at its output, so matching networks or circuits arerequired to provide proper impedance transformation for multiplefrequency bands in order to reach low output impedance at its output indifferent modes. In addition, mismatch and asymmetry (e.g., amplitudedifference and/or phase difference) between the differential signals candegrade the output performance of the power amplifier.

Therefore, there is a need to design a matching network circuit andrelated matching network and power amplifier to achieve odd harmonicrejection in the differential mode, even harmonic rejection in thecommon mode, and symmetry improvement, so as to ensure the outputperformance of the power amplifier.

SUMMARY

It is therefore an objective of the present invention to provide amatching network circuit and radio-frequency power amplifier capable ofodd harmonic rejection and even harmonic rejection and method ofadjusting symmetry of differential signals.

The present invention discloses a matching network circuit for RF poweramplifier circuit capable of odd harmonic rejection and even harmonicrejection in the differential mode and the common mode, respectively.The matching network circuit includes a differential mode filter with adifferential resonant frequency and a passive component coupled to avirtual short circuit node at the differential mode filter, wherein acommon mode filter with a common resonant frequency includes thedifferential mode filter and the passive component. As a result, twonotch filters with different resonant frequencies are utilized for thecommon mode and the differential mode, respectively.

The present invention further discloses a method for adjusting thesymmetry of the differential signals in the radio-frequency poweramplifier. The method includes detecting power of the differentialsignals at the symmetry node of the matching network circuit, generatingat least one control signals according to the detected power, andadjusting the phase difference and amplitude difference between thedifferential signals in the stages (e.g., input, driver and core stages)prior to the matching stage where the matching network providesimpedance tuning and matching. Therefore, the symmetry of thedifferential signals can be improved to reach better output performanceof the RF power circuit.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a matching network circuit andcorresponding equivalent circuits in differential mode and common mode.

FIG. 2 illustrates a schematic diagram of a matching network circuit andcorresponding equivalent circuits in differential mode and common modeaccording to an embodiment of the present invention.

FIG. 3 and FIG. 4 illustrate frequency response simulations of thematching network circuit corresponding to selective inductances andcapacitances according to different embodiments of the presentinvention.

FIG. 5 is a schematic diagram of a matching network according to anembodiment of the present invention.

FIG. 6 illustrates three different unit sections with differentsuppression purposes in a matching network according to an embodiment ofthe present invention.

FIG. 7 is a flowchart of a process according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a schematic diagram of a matching network circuit 10and corresponding equivalent circuits in differential (odd) mode andcommon (even) mode. The matching network circuit 10 is utilized in aradio-frequency (RF) amplifier, and includes two capacitors C₁, aninductor L₁, differential input nodes A and A′ , and a node B. An RFinput signal is split into either two identical signals in the commonmode or two signals with 180-degree out-of-phase from one another in thedifferential mode, to be inputted in the differential input nodes A andA′, respectively. The matching network circuit 10 is structurallysymmetric about the node B. The capacitors C₁ are coupled between thenode B and the differential input nodes A and A′ respectively, and theinductor L₁ is coupled between the node B and a ground.

In the differential mode, because of presence of perfect electric wallat the node B, the node B operates as a virtual short circuit or virtualground, thereby the centrally loaded components L₁ at the node B becomesshort-circuited. In such a situation, the inductor L₁ can be neglectedsince both ends thereof are short-circuited, so half of the matchingnetwork circuit 10 is equivalent to the capacitor C₁ coupled to theground (or zero amplitude). The capacitor C₁ can be shunted to anotherinductor to form an LC resonator or a lowpass filter, and an LC value ofthe LC resonator can be determined according to a fundamental frequencyof the differential RF input signal for impedance matching.

In the common mode, because of presence of perfect magnetic wall at thenode B, the node B operates as a virtual open circuit, thereby thecentrally loaded component L₁ at the node B becomes open-circuited.Moreover, an overall electrical length of the centrally loaded componentL₁ at the node B is increased due to the virtual open circuit, where theinductor L₁ is equivalent to two parallel inductors with doubleinductance of the inductor L₁. In such a situation, half of the matchingnetwork circuit 10 is equivalent to the capacitor C₁ in series withdouble the inductor L₁ coupled to the ground, and operates as an LCresonator or a notch filter with a common mode resonant frequency, whichcan be denoted as the equation (1.1).

$\begin{matrix}{\omega_{L,{even}} = \frac{1}{\sqrt{2L_{1}C_{1}}}} & \left( {1 - 1} \right)\end{matrix}$

where ω_(L,even) (represents the common mode resonant angular frequencywhich is denoted as 2πf, where f represents frequency. Note that theterm. “resonant frequency” represents the “resonant angular frequency”in this patent.

According to the equation (1.1), even harmonics of the RF input signalwith the common mode resonant frequency can be filtered out or rejectedin the common mode.

FIG. 2 illustrates a schematic diagram of a matching network circuit 20and corresponding equivalent circuits in differential mode and commonmode according to an embodiment of the present invention. The matchingnetwork circuit 20 is utilized in a radio-frequency (RF) amplifier, andincludes the two capacitors C₁, an inductor L₂, two inductors L₃, thedifferential input nodes A and A′, and a node C. The RF input signal issplit into either two identical signals in the common mode or twosignals with 180-degree out-of-phase from one another in thedifferential mode, to be inputted in the differential input nodes A andA′ respectively. The matching network circuit 20 is structurallysymmetric about the node C. The capacitors C₁ are coupled between theinductors L₃ and the differential input nodes A and A′ respectively, theinductors L₃ are coupled between the capacitors C₁ and the node Crespectively, and the inductor L₂ is coupled between the node C and theground.

In the differential mode, because of presence of perfect electric wallat the node C, the node C operates as a virtual short circuit or virtualground, thereby the centrally loaded component L₂ at the node C becomesshort-circuited. In such a situation, the inductor L₂ can be neglectedsince both ends thereof are short-circuited, so half of the matchingnetwork circuit 20 is equivalent to the capacitor C₁ in series with theinductor L₃ coupled to the ground. In such a situation, half of thematching network circuit 20 operates as an LC resonator or a notchfilter with a differential mode resonant frequency.

In the common mode, because of presence of perfect magnetic wall at thenode C, the node C behaves as a virtual open circuit, thereby thecentrally loaded component L₂ at the node C becomes open-circuited.Moreover, an overall electrical length of the centrally loaded componentL₂ at the node C is increased due to the virtual open circuit, where theinductor L₂ is equivalent to two parallel inductors with doubleinductance of the inductor L₂. In such a situation, half of the matchingnetwork circuit 20 is equivalent to the capacitor C₁ in series with theinductor L₃ and double of the inductor L₂ coupled to the ground, andoperates as an LC resonator or a notch filter with a common moderesonant frequency.

The common mode resonant frequency and the differential mode resonantfrequency for half of the matching network circuit 20 can berespectively denoted as the equations (2.1) and (2.2).

$\begin{matrix}\left\{ \begin{matrix}{\omega_{L,{even}} = \frac{1}{\sqrt{\left( {{2L_{2}} + L_{3}} \right)C_{1}}}} \\{\omega_{H,{odd}} = \frac{1}{\sqrt{L_{3}C_{1}}}}\end{matrix} \right. & \left( {2.1;2.2} \right)\end{matrix}$

where ω_(L,even) is the common mode resonant frequency, ω_(H,odd) is thedifferential mode resonant frequency.

According to the equations (2.1) and (2.2), even harmonics of the RFinput signal with the common mode resonant frequency can be filtered outor rejected in the common mode, and odd harmonics of the RF input signalwith the differential mode resonant frequency can be filtered out orrejected in the differential mode. Therefore, the matching networkcircuit 20 achieves odd harmonic rejection and even harmonic rejectionin the differential mode and the common mode, respectively.

Note that the common mode resonant frequency is lower than thedifferential mode resonant frequency. In detail, according to theequations (2.1) and (2.2), the resonant frequency is negativelyproportional to an effective inductance based on the same capacitance ofthe capacitor C₁. The effective inductance (2L₂+L₃) for even harmonicrejection is higher than the effective inductance L₃ for odd harmonicrejection, which makes the common mode resonant frequency to be lowerthan the differential mode resonant frequency.

Further, given a ratio k of the inductances of the inductors L₂ and L₃,wherein the ratio k is a real number to be adjustable according topractical requirements. Based on the equations (2.1) and (2.2), theratio k is rewritten in the equation (2.3).

$\begin{matrix}{\frac{L_{2}}{L_{3}} = {\frac{\omega_{H,{odd}}^{2} - \omega_{L,{even}}^{2}}{2\omega_{L,{even}}^{2}} = k}} & (2.3)\end{matrix}$

According to the equation (2.3), once the target resonant frequenciesfor odd and even harmonic rejections are determined, the ratio k can bedetermined, and the inductances of the inductor L₂ and L₃ can bedesigned based on the capacitance of the capacitor C₁ (which is givenbased on the impedance matching for the fundamental frequency).

Given that the capacitance of the capacitor C₁ and the common moderesonant frequency are the same in both the matching network circuits 10and 20, and a condition is derived according to the equation (1.1) andthe equation (2.1), which is denoted as the equation (2.4).

2L ₁=2L ₂ +L ₃-   (2.4)

The inductances of the inductor L₂ and L₃ can be described by the ratiok and the inductance of the inductor L₁ in the equations (2.5) and(2.6), respectively.

$\begin{matrix}\left\{ \begin{matrix}{L_{2} = {\frac{2k}{{2k} + 1}L_{1}}} \\{L_{3} = {\frac{2}{{2k} + 1}L_{1}}}\end{matrix} \right. & \left( {2.5;2.6} \right)\end{matrix}$

According to the equations (2.4), (2.5) and (2.6), for half of thematching network circuit 20, a total required inductance for the commonmode resonant frequency is denoted as

${L_{2} + {2L_{3}}} = {\frac{{2k} + 4}{{2k} + 1}{L_{1}.}}$

In the matching network circuit 10, there is only one notch filtercreated for the common mode, which is realized by the capacitor C₁ andthe inductor L₁. In comparison, in the matching network circuit 20, twonotch filters are created respectively for the common mode and thedifferential mode, which are realized by the capacitor C₁ and theinductors L₂ and L₃. Specifically, a notch filter for the common mode isrealized by the capacitor C₁ and the inductors L₂ and L₃, and anothernotch filter for the differential mode is realized by the capacitor C₁and the inductor L₃.

From another point of view, since the symmetry node of the matchingnetwork circuit operates as the virtual short circuit in thedifferential mode and operates as the virtual open circuit in the commonmode, the electrical characteristics of the central loaded component(e.g., passive component) is changed between the differential mode andthe common mode. With this change, the shunted LC resonator constitutedby the capacitor C₁ and the inductor L₃ operates as a differential modefilter with a differential resonant frequency, and the central loadedcomponent (i.e., the inductor L₂ coupled between the ground and thevirtual short node C at the differential mode notch filter) and thedifferential mode filter constitute a common mode filter with a commonresonant frequency. As a result, the matching network circuit canachieve odd harmonic rejection and even harmonic rejection in thedifferential mode and the common mode, respectively.

The inductances and capacitances of the components comprised in thematching network circuit can be properly selected according to theequations (2.1) to (2.6) and further taking any matching conditions andrejection conditions into considerations for various applications andtarget frequencies, which is not limited.

For example, FIG. 3 and FIG. 4 illustrate frequency response simulationsof the matching network circuit 20 corresponding to selectiveinductances and capacitances according to different embodiments of thepresent invention. FIG. 3 and FIG. 4 illustrate an insertion loss in thecommon mode (S21_Even denoted with thick line with circles), aninsertion loss in the differential mode (S21_Odd denoted with thin linewith circles), a return loss in the common mode (S11_Even denoted withthick line), and a return loss in the differential mode (S11_Odd denotedwith thin line).

In FIG. 3, given that a fundamental frequency is about 1 GHz, an evenharmonic (i.e., common mode resonant frequency) of the fundamentalfrequency is about 2 GHz, and an odd harmonic (i.e., differential moderesonant frequency) of the fundamental frequency is about 3 GHz.

In the common mode, the return loss is low at the fundamental frequency(1 GHz), and the insertion loss shows a notch at the even harmonic (2GHz), which means that the RF signal at the fundamental frequency iswell matched, and the even harmonic of the RF signal are rejected. Inthe differential mode, the return loss is low at the fundamentalfrequency (1 GHz), and the insertion loss shows a notch at the oddharmonic (3 GHz), which means that the RF signal at the fundamentalfrequency is well matched, and the odd harmonic of the RF signal isrejected in the differential mode.

As a result, in the differential mode and the common mode, the matchingnetwork circuit can achieve even harmonic rejection, odd harmonicrejection as well as impedance matching for the fundamental frequency.

In FIG. 4, given that a fundamental frequency is about 1 GHz, an evenharmonic (i.e., common mode resonant frequency) of the fundamentalfrequency is about 3 GHz, and an odd harmonic (i.e., differential moderesonant frequency) of the fundamental frequency is about 5 GHz.

In the common mode, the return loss is low at the fundamental frequency(1 GHz), and the insertion loss shows a notch at the even harmonic (3GHz), which means that the RF signal at the fundamental frequencymatches with the matching network circuit, and the even harmonic of theRF signal are rejected in the common mode. In the differential mode, thereturn loss is low at the fundamental frequency (1 GHz), and theinsertion loss shows a notch at the odd harmonic (5 GHz), which meansthat the RF signal at the fundamental frequency is well matched, and theodd harmonic of the RF signal is rejected in the differential mode.

As a result, in the differential mode and the common mode, the matchingnetwork circuit can achieve even harmonic rejection, odd harmonicrejection as well as impedance matching for the fundamental frequency.

In short, the matching network circuit of present invention includes adifferential mode filter with a differential resonant frequency and apassive component coupled to the virtual short circuit node at thedifferential mode filter, where a common mode filter with a commonresonant frequency is constituted by the differential mode filter andthe passive component. As a result, the matching network circuit canachieve odd harmonic rejection and even harmonic rejection in thedifferential mode and the common mode, respectively. Those skilled inthe art can make modifications and alterations accordingly, which is notlimited.

FIG. 5 is a schematic diagram of a matching network 50 according to anembodiment of the present invention. The matching network 50 includescapacitors C_(1o), C_(2o), C_(3o), C_(1e) and C_(3e), inductors L_(1o),L_(2o), L_(3o), L_(2e), L_(3e), L_(1f) and L_(2f), differential inputnodes A and A′, differential output nodes G and G′, differentialintermediate nodes H and H′, and symmetry nodes D, E and F. The matchingnetwork 50 is structurally symmetric about the nodes D, E and F whichbehave as a virtual short circuit in the differential mode, and behaveas a virtual open circuit in the common mode. The matching network 50 isgeneric from an LC lowpass matching network, where the inductors L_(1f)and L_(2f) are used for impedance matching for the RF signal.

The capacitors C_(1o) and C_(1e) and the inductor L_(1o) constitute afirst-stage matching network circuit shunted between the signal paths ofthe differential signals (or the differential input nodes A and A′). Thecapacitor C_(1o) and the inductor L_(1o) operate as a differential modefilter with a differential resonant frequency f_(1o), the capacitorC_(1e) is coupled to the node D, and the capacitors C_(1o) and C_(1e)and the inductor L_(1o) operate as a common mode filter with a commonresonant frequency f_(1e).

Note that the common mode resonant frequency f_(1e) is higher than thedifferential mode resonant frequency f_(1o). In detail, in light of theequations (2.1) and (2.2), the resonant frequency is negativelyproportional to an effective capacitance based on the same inductance ofthe inductor L_(1o). The effective capacitance contributed by thecapacitor C_(1o) in series with the capacitor C_(1e), where an overallcapacitance of them is decreased for even harmonic rejection, is smallerthan the effective capacitance C_(1o) for odd harmonic rejection, whichmakes the common mode resonant frequency f_(1e) to be higher than thedifferential mode resonant frequency f_(1o).

The capacitors C_(2o) and the inductors L_(2o) and L_(2e) constitute asecond-stage matching network circuit shunted between the signal pathsof the differential signals (or the differential intermediate nodes Hand H′). The capacitor C_(2o) and the inductor L_(2o) operate as adifferential mode filter with a differential resonant frequency f_(2o),the inductor L_(2e) is coupled to the node E, and the capacitor C_(2o)and the inductors L_(2o) and L_(2e) operate as a common mode filter witha common resonant frequency f_(2e). The second matching unit has anidentical structure as the matching network circuit 20, and the commonmode resonant frequency f_(2e) is lower than the differential moderesonant frequency f_(2o) due to the inductor L_(2e).

The capacitors C_(3o) and C_(1e) and the inductors L_(3o) and L_(3e)constitute a third-stage matching network circuit shunted between thesignal paths of the differential signals (or the differential outputnodes G and G′). The capacitor C_(3o) and the inductor L_(3o) operate asa differential mode filter with a differential resonant frequencyf_(3o), an LC resonator formed by the inductor L_(3e) and the capacitorC_(3e) is coupled to the node F, and the capacitors C_(3o) and C_(3e)and the inductors L_(3o) and L_(3e) operate as a common mode filter witha common resonant frequency f_(3e).

Note that the common mode resonant frequency f_(3e) can be either higheror lower than the differential mode resonant frequency f_(3o). Indetail, in light of the equations (2.1) and (2.2), the resonantfrequency is negatively proportional to a product of effectivecapacitance and effective inductance (or effective LC value). The LCresonator formed by the inductor L_(3e) and the capacitor C_(3e) caneither decrease or increase the effective LC value based on theirvalues, which makes the common mode resonant frequency f_(3e) to beeither higher or lower than the differential mode resonant frequencyf_(3o).

The LC resonator formed by the inductor L_(3e) and the capacitor C_(3e)is further used for common mode impedance tuning. Specifically, thethird-stage matching network circuit is shunted between differentialoutput nodes G and G′ to influence an output impedance of the matchingnetwork 50. In the matching network 50, all components which are coupledto virtual short/open node can adjust the common mode output impedancewithout affecting differential mode output impedance. Since the inductorL_(3e) and the capacitor C_(3e) are effective only in the common mode,the common mode output impedance of the matching network 50 isinfluenced by the inductor L_(3e) and the capacitor C_(3e). Hence, theirLC value of the inductor L_(3e) and the capacitor C_(3e) should beselected by taking the common mode output impedance into consideration.

In one embodiment, the order or locations of the first-stage,second-stage and third-stage matching network circuits can be adjustedaccording to practical requirement, which is not limited. Or, thepassive components of the matching network circuits can be replaced byany types of passive components, which is not limited.

FIG. 6 illustrates three different unit sections with differentsuppression purposes in a matching network of a RF power circuit 6according to an embodiment of the present invention. Operations of theRF power circuit 6 can be divided into several stages such as inputstage, power amplifier (PA) driver stage, PA core stage, matching stageand output stage. In the input stage, the RF signal is inputted to aninput node to be split by an input splitter into a pair of differentialsignals. The phase tuner provides any phase difference adjustmentbetween in-phase signal path and 180-degree out-of-phase path. Forexample, if the ideal phase delays before phase tuners are 0° atin-phase path and 180° at 180-degree out-of-phase path, the phase delayswill become 0°+Δθ_(in-phase) and 180°+Δθ_(out-phase) where Δθ_(in-phase)and Δθ_(out-phase) can be any additional phase delay from phase tuner.In the PA driver stage, a pair of power amplifiers 607 and 608 amplifiesthe differential signals with the same or different bias gains,respectively. In the PA core stage, a pair of power amplifiers 605 and606 amplifies the differential signals with the same or different gains,respectively. In the matching stage, a matching network 60 providesimpedance matching between the PA core stage and the output stage, whereodd harmonic and even harmonic signals of the RF signal can be rejectedby the matching network 60. In the output stage, the differentialsignals are converted into a single-ended signal by using an outputtransformer.

In FIG. 6, the RF power circuit 6 includes the matching network 60, apower detector 600, adjusting circuits 601-604, and the power amplifiers605-608. In structure, the power detector 600 is coupled to a symmetrynode (i.e. node I) of the matching network 60, the adjusting circuits601-604, and the power amplifiers 605-608. The adjusting circuits 601and 602 are coupled to the signal paths for the differential signalsbetween the phase tuner and the power amplifiers 607 and 608. Theadjusting circuits 603 and 604 are coupled to the signal paths for thedifferential signals between a PA driver stage phase tuner and the poweramplifiers 605 and 606.

In operation, the power detector 600 detects a signal at the symmetrynode I, and then generates at least one control signal according to thedetected signal. The power detector 600 further outputs the at least onecontrol signal to at least one of the adjusting circuits 601-604 and thepower amplifiers 605-608 at the previous stages prior to the matchingstage, so as to adjust electric characteristics (including at least oneof phase, amplitude, voltage, current and power) of the differentialsignals, thereby improve the symmetry of the differential signals. Eachof the adjusting circuits 601-604 includes a phase shifter and anattenuator, where the phase shifter delays at least one of thedifferential signals to adjust the phase difference of the differentialsignals, and the attenuator attenuates at least one of the differentialsignals to adjust the amplitude difference of the differential signals.The power gain provided by the power amplifiers 605-608 can becontrolled independently according to the control signal.

As can be seen in FIG. 6, the RF power circuit 6 provides a close-loopstructure between the matching network 60, the power detector 600 andthe adjusting circuits 601-604. With the close-loop structure, the phasedifference and the amplitude difference between the differential signalscan be eliminated by adjusting the electric characteristics of thedifferential signals at the previous stages according to the detectedsignal at the later matching stage. In practice, such adjustment can beiteratively performed until the symmetry of the differential signals issatisfied, and hence the differential signals can be well matched. Notethat detecting the signal at the symmetry node has a smaller loss impactthan detecting the signal at the signal paths of the differentialsignals.

In one embodiment, the power detector 600 is frequency selective toadjust the symmetry of the differential signals for specific harmonicfrequency. For example, the power detector 600 detects the signal withthe differential resonant frequency (i.e., odd harmonic frequency) inthe differential mode or with the common resonant frequency (i.e., evenharmonic frequency) in the common mode.

Further, when performing the detection, even harmonic power is expectedto be as large as possible, and odd harmonic power is expected to be assmall as possible. Specifically, the symmetry node I behaves as thevirtual open circuit in the common mode, and the common mode notchfilter resonates the even harmonic, so the signal swing (power oramplitude) of the even harmonic observed at the symmetry node I shouldbe large. On the other hand, the symmetry node I behaves as the virtualshort circuit in the differential mode, so the signal swing (power oramplitude) of the odd harmonic observed at the symmetry node I should besmall. The signal swing of odd harmonic observed at the symmetry node issmall because the virtual short provides very low impedance.

In one embodiment, additional power detectors can be put at othersymmetry nodes of the matching network 60 to detect electriccharacteristics of the differential signals, and adjust at least one ofthe amplitude difference and phase difference between the signal pathsat the previous stages for better output performance.

Operations of the RF power circuit 6 for adjusting the symmetry of thedifferential signals can be summarized in to a process 70 as shown inFIG. 7, and the process 70 includes the following steps.

Step 700: Start.

Step 701: Detect power of differential signal for odd harmonic or commonmode signal for even harmonic at a symmetry node of a matching network.

Step 702: Generate at least on control signal according to the power ofdetected signal.

Step 703: Adjust phase difference and amplitude difference between thedifferential signals in previous stages prior to the matching networkaccording to the at least one control signal.

Step 704: End.

In the process 70, Steps 701 and 702 are performed by the powerdetector, and Step 703 is performed by at least one of the adjustingcircuit and the power amplifiers. Note that in Step 703, the phasedifference and amplitude difference between the differential signals areadjusted in the stages (e.g., input, driver and core stages) prior tothe matching stage where the matching network provides impedance tuningand matching. By the process 70, the symmetry of the differentialsignals can be improved for better output performance of the RF powercircuit.

To sum up, the matching network circuit of present invention includes adifferential mode filter with a differential resonant frequency and apassive component coupled to the virtual short circuit node at thedifferential mode filter, thereby a common mode filter with a commonresonant frequency is constituted by the differential mode filter andthe passive component. As a result, the matching network circuit canachieve odd harmonic rejection and even harmonic rejection in thedifferential mode and the common mode, respectively. In addition, thepresent invention provides a method for adjusting the symmetry of thedifferential signals, which detects power of the differential signals orthe common mode signals at the symmetry node of the matching networkcircuit to adjust the phase difference and amplitude difference betweenthe differential signals in the stages (e.g., input, driver and corestages) prior to the matching stage where the matching network providesimpedance tuning and matching. Therefore, the symmetry of thedifferential signals can be improved for better output performance ofthe RF power circuit.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A matching network circuit, applied to a radio-frequency (RF) power amplifier processing an RF input signal, comprising: a first input node for receiving a first signal component of the RF input signal; a second input node for receiving a second signal component of the RF input signal; a first output node, wherein a first signal path of the first signal component of the RF input signal is formed between the first input node and the first output node; a second output node, wherein a second signal path of the second signal component of the RF input signal is formed between the second input node and the second output node; a symmetry node; a first differential mode notch filter with a differential resonant frequency, coupled between the first signal path of the first signal component of the RF input signal and the symmetry node; a second differential mode notch filter with the differential resonant frequency, coupled between the second signal path of the second signal component of the RF input signal and the symmetry node; and a passive network circuit, comprising a first passive component, coupled to a ground and the symmetry node; wherein a common mode notch filter with a common resonant frequency comprises the passive network circuit and one of the first and second differential mode notch filters.
 2. The matching network circuit of claim 1, wherein the passive component comprises a capacitor, and the common resonant frequency is higher than the differential resonant frequency.
 3. The matching network circuit of claim 1, wherein the passive component comprises an inductor, and the common resonant frequency is lower than the differential resonant frequency.
 4. The matching network circuit of claim 1, wherein the passive component comprises an LC resonator, and the common resonant frequency is decided according to an LC value of LC resonator.
 5. The matching network circuit of claim 4, wherein the LC resonator is used for common mode impedance tuning of an output impedance of the differential matching network.
 6. The matching network circuit of claim 1, wherein the differential mode notch filter comprises an LC resonator.
 7. The matching network circuit of claim 1, wherein the symmetry node operates as a virtual short circuit if the matching network circuit operates in a differential mode, and matching network circuit operates as a virtual open circuit if the matching network circuit operates in a common mode.
 8. The matching network of claim 1, wherein the first and second signal components of the RF signal comprise a pair of differential signals.
 9. The matching network of claim 1, wherein the first and second input nodes are coupled to a power amplifier core stage circuit of the RF power amplifier, and the first and second output nodes are coupled to an output stage circuit of the RF power amplifier.
 10. A radio-frequency (RF) power amplifier, comprising: a matching network comprising at least one matching network circuit corresponding to at least one symmetry node, for receiving an RF signal amplified by the RF power amplifier; at least one detector, coupled to the at least one symmetry node corresponding to the at least one matching network circuit, for detecting power of a detected signal at the symmetry node of the matching network, and generating at least on control signal according to the power of the detected signal, wherein the detected signal is an odd harmonic of the RF signal when the RF power amplifier operates in a differential mode or an even harmonic of the RF signal when the RF power amplifier operates in a common mode; and at least one adjusting circuit, coupled to the power detector, for adjusting the RF signal according to the at least one control signal.
 11. The RF power amplifier of claim 10, wherein the at least one detector is a power detector, a voltage detector, or a current detector, and the at least one signal corresponds to a power, a voltage or a current of the detected signal.
 12. The RF power amplifier of claim 10, wherein the at least one detector is frequency selective to detect the detected signal with a differential resonant frequency in the differential mode or with a common resonant frequency in the common mode.
 13. The RF power amplifier of claim 10, further comprising: an input stage circuit, for splitting the RF signal into the differential signals; a driver stage circuit, coupled to the input stage circuit, for respectively amplifying the differential signals; a core stage circuit, coupled between the driver stage circuit and the differential matching network, for respectively amplifying the differential signals; and an output stage circuit, coupled to the differential matching network, for converting the differential signals into a single-ended output signal.
 14. The RF power amplifier of claim 13, wherein the driver stage circuit comprises a pair of power amplifiers, coupled to the at least one detector, for respectively amplifying the differential signals by a first bias gain and a second bias gain, wherein the pair of power amplifiers changes at least one of the first and second bias gains according to the at least one control signal.
 15. The RF power amplifier of claim 13, wherein the core stage circuit comprises a pair of power amplifiers, coupled to the at least one detector, for respectively amplifying the differential signals by a first core gain and a second core gain, wherein the pair of power amplifiers changes at least one of the first and second core gains according to the at least one control signal.
 16. The RF power amplifier of claim 13, wherein the at least one adjusting circuit is coupled to at least one of the input stage circuit, the driver stage circuit, and the core stage circuit.
 17. The RF power amplifier of claim 10, wherein the at least one adjusting circuit comprises: a phase shifter, coupled to one of signal paths of the differential signals and the at least one detector, for delaying at least one of the differential signals according to the at least one control signal; and an attenuator, coupled to one of signal paths of the differential signals and the at least one detector, for attenuating at least one of the differential signals according to the at least one control signal.
 18. The RF power amplifier of claim 10, wherein the at least one matching network circuit comprises: a first input node for receiving a first signal component of the RF input signal; a second input node for receiving a second signal component of the RF input signal; a first output node, wherein a first signal path of the first signal component of the RF input signal is formed between the first input node and the first output node; a second output node, wherein a second signal path of the second signal component of the RF input signal is formed between the second input node and the second output node; a symmetry node; a first differential mode notch filter with a differential resonant frequency, coupled between the first signal path of the first signal component of the RF input signal and the symmetry node; a second differential mode notch filter with the differential resonant frequency, coupled between the second signal path of the second signal component of the RF input signal and the symmetry node; and a passive network circuit, comprising a first passive component, coupled to a ground and the symmetry node; wherein a common mode notch filter with a common resonant frequency comprises the passive network circuit and one of the first and second differential mode notch filters.
 19. The matching network circuit of claim 18, wherein the symmetry node behaves as a virtual short circuit if the matching network circuit operates in a differential mode, and matching network circuit behaves as a virtual open circuit if the matching network circuit operates in a common mode.
 20. The matching network of claim 18, wherein the first and second signal components of the RF signal are a pair of differential signals.
 21. The matching network of claim 18, wherein the first and second input nodes are coupled to a power amplifier core stage circuit of the RF power amplifier, and the first and second output nodes are coupled to an output stage circuit of the RF power amplifier.
 22. A method of adjusting symmetry of differential signals for a radio-frequency (RF) power amplifier, comprising: detecting power of a detected signal at a symmetry node of the matching network; generating at least on control signal according to the power of the detected signal, wherein the detected signal is an odd harmonic of an RF signal when the RF power amplifier operates in a differential mode or an even harmonic of the RF signal when the RF power amplifier operates in a common mode; and adjusting the RF signal according to the at least one control signal.
 23. The method of claim 22, wherein detecting the power of the detected signal at a symmetry node of the matching network comprises: detecting the power of the detected signal with a differential resonant frequency in the differential mode or with a common resonant frequency in the common mode.
 24. The method of claim 22, wherein adjusting phase difference and amplitude difference between the differential signals according to the at least one control signal comprises: respectively amplifying the differential signals by a first gain and a second gain according to the at least one control signal.
 25. The method of claim 22, wherein adjusting phase difference and amplitude difference between the differential signals according to the at least one control signal comprises: delaying at least one of the differential signals according to the at least one control signal.
 26. The method of claim 22, wherein adjusting phase difference and amplitude difference between the differential signals according to the at least one control signal comprises: attenuating at least one of the differential signals according to the at least one control signal.
 27. The method of claim 22, wherein the RF power amplifier comprises an input stage circuit, a driver stage circuit and a core stage circuit, and the at least one of the phase difference and the amplitude difference is adjusted in at least one of the input stage circuit, the driver stage circuit and the core stage circuit. 